74HC191 is an asynchronously presettable 4-bit binary up/down counter. It contains fourmaster/slave flip-flops with internal gating and steering logic to provide asynchronous preset andsynchronous count-up and count-down operation.
Asynchronous parallel load capability permitsthe counter to be preset to any desired value. Information present on the parallel data inputs (D0to D3) is loaded into the counter and appears on the outputs when the parallel load (PL) input isLOW. This operation overrides the counting function.
Counting is inhibited by a HIGH level on thecount enable (CE) input. When CE is LOW internal state changes are initiated synchronously bythe LOW-to-HIGH transition of the clock input. The up/down (U/D) input signal determines thedirection of counting as indicated in the function table.
The CE input may go LOW when the clock isin either state, however, the LOW-to-HIGH CE transition must occur only when the clock is HIGH.Also, the U/D input should be changed only when either CE or CP is HIGH.
Overflow/underflowindications are provided by two types of outputs, the terminal count (TC) and ripple clock (RC).The TC output is normally LOW and goes HIGH when a circuit reaches zero in the count-downmode or reaches '15' in the count-up-mode. The TC output will remain HIGH until a state changeoccurs, either by counting or presetting, or until U/D is changed. Do not use the TC output as aclock signal because it is subject to decoding spikes.
- Logic type : 4-Bit Counter.
- Low Input Current of 1 μA Max
- Supply Voltage : 2 -6V.
- Package type : DIP 16.
- Asynchronously Presettable With Load Control.
- Operating Temperature Range: -40°C to +125°C.